1. Field of the Invention
The present invention relates to a mechanism for shifting ring bodies toward and away from each other and a mechanism for moving lens groups. In particular, the present invention relates to a mechanism for moving ring bodies or lens groups via an end-faced cam surface.
2. Description of the Related Art
The assignee of the present application has proposed an unprecedented zoom lens system that meets the contradictory demands of high zoom ratio and miniaturization (U.S. patent application Ser. No. 09/534,307, now U.S. Pat. No. 6,369,955, Japanese Patent Application No. Hei 11-79572). This zoom lens system has the following characteristics: it includes a plurality of movable lens groups for varying the focal length; at least one of the lens groups is a switching lens group which includes two sub-lens groups, one of the sub-lens groups being a movable sub-lens group that can be selectively positioned at either one movement extremities in the optical axis direction with respect to the other sub-lens group; the movable sub-lens group of the switching lens group is positioned at an extremity of a short-focal-length zooming range, from the short focal length extremity to an intermediate focal length, and at the opposite extremity of a long-focal-length zooming range, from the intermediate focal length to a long focal length extremity; and zoom paths of the switching lens group and the other lens groups are discontinuous at the intermediate focal length and are defined to focus on a predetermined image plane corresponding to the position of the movable sub-lens group. There may be one or more intermediate focal lengths.
When selecting or designing a mechanism for moving ring bodies (such as a lens group frames) with emphasis on a particular virtue of the mechanism, e.g., simplicity, the same mechanism may have other drawbacks, e.g., the simple mechanism may not have the preferred amount or optimum amount of strength, or the simple mechanism may have gaps through which light can enter the system. It may not be desirable, however, to provide a separate member for reinforcement and/or light-shielding purposes in view of space required to provide such construction as well as in view of the manufacturing cost.
It is an object of the present invention to provide a shift mechanism as well as a lens group shift mechanism that achieves improved strength and light-shielding ability without sacrificing simple construction.
In order to achieve the above-mentioned object, a shift mechanism for shifting two ring members is provided, the shift mechanism including a first ring body and a second ring body which can be rotated relative to each other about a common axis, at least one of the first and second ring bodies being movable in a direction of the common axis; a shift cam surface formed on the first ring body on an end surface thereof which faces the second ring body, the shift cam surface being inclined with respect to a circumferential direction of the first ring body; a follower projection formed on the second ring body for engaging with the shift cam surface; and a rotating mechanism for rotating the first and second ring bodies relative to each other. The shift cam surface and the follower projection are arranged to move the first and second ring bodies toward and away from each other in the axial direction as the first and second ring bodies are rotated relative to each other. An annular rib is formed along the circumference of the first ring body radially outside the shift cam surface to extend toward the second ring body over the follower projection of the second ring body.
Preferably, an inner surface of the annular rib of the first ring body is slidably in contact with a portion of an outer surface of the second ring body.
In an embodiment, the follower projection is formed on the second ring body on one end surface thereof which faces the first ring body, and a second annular rib, which differs from the annular rib of the first ring body, is formed along the circumference of the second ring body radially inside the follower projection to extend toward the first ring body.
Preferably, the first and second ring bodies include a first sub-lens group frame and a second sub-lens group frame for supporting a first sub-lens group and a second sub-lens group, respectively, the first and second sub-lens groups functioning optically in a mutually close position and in a mutually distant position, with respect to the optical axis thereof.
Preferably, one of the first and second ring bodies includes a focusing lens support member for supporting a focusing lens group so as to move in the axial direction; and the other of the first and second ring bodies includes an actuator ring that can rotate relative to the focusing lens support member, the rotation of the actuator ring causing the focusing lens support member to move in the axial direction via the shift cam surface and the follower projection.
Preferably, the focusing lens support member includes a first sub-lens group frame and a second sub-lens group frame which support a first sub-lens group and a second sub-lens group, respectively, and are able to rotate and move in the axial direction with respect to each other, the first and second sub-lens groups functioning optically in a mutually close position and in a mutually distant position, with respect to the optical axis thereof.
According to another aspect of the present invention, a lens displacement mechanism is provided, including a first sub-lens group and a second sub-lens group functioning optically in a mutually close position and in a mutually distant position, with respect to the optical axis thereof; a first sub-lens group frame and a second sub-lens group frame which support the first sub-lens group and the second sub-lens group, respectively, the first and second sub-lens group frames being rotatable about a common axis and movable in a direction of the axis, with respect to each other; a shift cam surface formed on the first sub-lens group frame on an end surface thereof which faces the second sub-lens group frame, the shift cam surface being inclined with respect to a circumferential direction of the first sub-lens group frame; a shift follower projection formed on the second sub-lens group frame for engaging with the shift cam surface; and an actuator ring for rotating the first and second sub-lens group frames relative to each other. The shift cam surface and the shift follower projection are arranged to move the first and second sub-lens group frames to the mutually close position and to the mutually distant position as the first and second sub-lens group frames are rotated relative to each other. An annular rib is formed along the circumference of the first sub-lens group frame radially outside the shift cam surface to extend toward the second sub-lens group frame over the shift follower projection of the second sub-lens group frame.
Preferably, an inner surface of the annular rib of the first sub-lens group frame is slidably in contact with part of an outer surface of the second sub-lens group frame.
Preferably, the shift follower projection is formed on the second sub-lens group frame on one end surface thereof which faces the first sub-lens group frame, and a second annular rib which differs from the annular rib of the first sub-lens group frame is formed along the circumference of the second sub-lens group frame radially inside the shift follower projection to extend toward the first sub-lens group frame.
Preferably, the first and second sub-lens groups form one of a plurality of variable lens groups of a zoom lens system which are moved in the optical axis direction during zooming, the first and second sub-lens groups serving as a focus lens group when in the mutually close position and when in the mutually distant position. A focusing mechanism is provided for moving the first sub-lens group frame and the second sub-lens group frame to the mutually close position and to the mutually distant position in the optical axis direction while maintaining the distance between the sub-lens group frames.
Preferably, the focusing mechanism includes a supporting barrel for supporting the first sub-lens group frame and the second sub-lens group frame, the first sub-lens group frame being supported in a manner that allows the first sub-lens group frame to move in the optical axis direction and prevents rotation thereof, the second sub-lens group frame being supported in a manner that allows the second sub-lens group frame to rotate between two rotational extremities over a predetermined angle and allows linear movement thereof in the optical axis direction, while preventing rotation thereof, at two rotational extremities thereof, each of the two rotational extremities corresponding to the mutually close position and the mutually distant position; a focus cam surface provided on the actuator ring on an end surface thereof which faces the second sub-lens group frame, the focus cam surface being inclined with respect to a circumferential direction of the actuator ring; and a focusing follower projection provided on the second sub-lens group frame for engaging with the focus cam surface at one of the two rotational extremities, the focusing follower projection being different from the shift follower projection for engaging with the shift cam surface of the first sub-lens group frame. The focus cam surface and the focusing follower projection of the second sub-lens group frame are arranged so as to move the second sub-lens group frame in the optical axis direction as the actuator ring is rotated.
Preferably, a second annular rib which differs from the annular rib of the first sub-lens group frame is formed along a circumference of the actuator ring radially outside the focus cam surface to extend toward the second sub-lens group frame over the focusing follower projection of the second sub-lens group frame.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 2000-289614 (filed on Sep. 22, 2000) which is expressly incorporated herein in its entirety.